Process and apparatus for straightening metallic rod stock



w. KORF Oct. 24, 1967 PROCESS AND APPARATUS FOR STRAIGHTENING METALLIC ROD STOCK Filed June lO, 1965 5 Sheets-Sheet 1 llw Q x .mi u

Oct. 24,`1'967 W KORF 3,348,400

PROCESS AND APPARATUS FOR STRAIGHTENING METALLlC ROD STOCK Filed June lO, 1965 3 Sheets-Sheet 2 Fig. 4

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Oct. 24, 1967 w. KORF 3,348,400

PROCSS AND APPARATUS FOR STRAIGHTENING METALLIC ROD STOCK Filed June lO, 1965 5 Sheets-Sheet 5 Fig.5

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United States Patent iice 3,348,400 Patented Oct. 24, 1967 3,348,400 PRCESS AND APPARATUS FOR STRAIGHTEN- NG METALLIC RGD STOCK Willy Kom, Baden-Baden, Germany, assignor to Ferrotest G.m.b.H., Basel (Schweiz), Germany Filed June 10, 1965, Ser. No. 462,954 Claims priority, application Germany, .lune 11, 1964, F 43,148 46 Claims. (Cl. '7216l) The present invention relates to treatment of coiled metallic rod stock, particularly to treatment of convoluted steel wire of the type which may be utilized in the production of reinforced concrete. Still more particularly, the invention relates to a process and apparatus for straightening coiled steel wire and similar metallic rod stock.

It is an important object of the present invention to provide a very simple process for straightening coiled steel wire and similar convoluted metallic rod stock.

Another object of the invention is to provide a process according to which steel wire or similar convoluted elongated metallic material may be straightened either continuously or at desired intervals, and according to which the stock may be straightened in such lengths as are needed for further processing, for example, in the manufacture of concrete reinforcing mats or similar products.

A further object of the invention is to provide a process of the above outlined characteristics according to which the straightening operation takes place simultaneously with highly desirable and substantial improvements in strength characteristics of the stock.

A concomitant object of the invention is to provide a process for straightening of coiled steel wire and for simultaneously improving tensile strength and/ or certain other characteristics of treated material.

Still another object of the invention is to provide a process according to which any desired length of coiled steel wire or similar metallic starting material may be straightened with utmost precision, by resorting to a relatively simple apparatus, and in a fully controlled manner so that the strength characteristics of the ultimate product are predictable with utmost accuracy.

An additional object of the invention is to provide a process of the above outlined characteristics according to which straightening and eventual changes in strength characteristics of treated material may take place simultaneously with controlled twisting or spinning of the stock.

Still another object of the instant invention is to provide a process which is particularly suited for straightening of coiled steel Wire of the type having longitudinally extending ribs or similar surface-enlarging projections which serve to insure stronger adherence of such stock to hardened concrete.

A further object of the invention is to provide a novel apparatus which may be utilized for practicing the above method and to construct and to assemble the apparatus in such a way that it can be used for continuous, intermittent or continuous and/or intermittent straightening of steel wire or the like.

Another object of the invention is to provide an apparatus of the just outlined characteristics which may he readily adjusted and converted for treatment of different types of steel wire or similar metallic rod stock, which may be constructed and assembled to operate in a fully automatic or in a semiautomatic way, and which may be -operated and supervised by semiskilled personnel.

An additional object of the invention is to provide a wire straightening apparatus which may be utilized for straightening of relatively thick or relatively thin wire, which may be used for straightening such material in sections of any desired and preferably variable length, and

which is not likely to deface or to otherwise damage the material of the wire even if such wire is provided with a large number of projections in the form of longitudinally extending ribs or the like.

A further object of the present invention is to provide an apparatus which may simultaneously subject a desired length of steel wire to two or more treatments including straightening, changes in strength characteristics and/or controlled spinning or twisting.

An adidtional object of the invention is to provide a novel clamping or gripping device which may be utilized in an apparatus of the above outlined characteristics and to construct the clamping device in such a way that the danger of damage to treated material is avoided in a very simple manner.

Still another object of the invention is to provide improved braking, stretching, flexing, cutting and feeding or advancing devices which may be utilized in the improved apparatus and to construct, mount and assemble such devices in a novel manner so that the apparatus may.

be readily and rapidly converted for automatic, semiautomatic or manual operation and that the apparatus may be rapidly transformed for treatment of ribbed or smoothsurfaced metallic stock and/or for treatment of largediameter or relatively thin wire or similar starting material.

A further object of my invention is to provide an apparatus which may be equipped Iwith automatic or semiautomatic storing, ejecting and similar devices which will stack or otherwise store straightened stock in a desired manner and which may be arranged to automatically deliver such stock to the next processing station, for example, to a machine which transforms straightened steel wire into concrete reinforcing mats or which feeds sections of straightened wire into a concrete mold.

Another object of the present invention is to provide a special type of steel wire which is especially suited for the production of concrete reinforcing mats and which may he treated with particular advantage in aocordance with my process and in an apparatus of the above outlined characteristics.

Briefly stated, one feature of my invention resides in the provision of a process for straightening convoluted metallic rod stock, particularly for straightening coiled steel wire of the type which is used in reinforced concrete and which is normally provided with longitudinally extending ribs or similar surface-enlarging projections. In its basic form, the process comprises the steps of uncoiling a section from a source of supply of such rod stock and flexing each zone of the section back and forth in at least one plane to effect partial straightening of the thus exed section, and thereupon subjecting the section to the action of tensional stresses of such magnitude that the overall length of the section increases by at least 2 percent with resultant straightening of the thus stretched section.

If the improved process is used mainly or exclusively for straightening of coil stock, the increase in length of any given section may be in the range of 2-6 percent. However, if the stretching step should improve the strength characteristics, and particularly the tensile strength of a section, the increase in length is normally between 4l2 percent, preferably between 6-11 percent and most preferably between 8-10 percent.

My improved process is of especially great economic importance in the mass production of concrete reinforcing mats or similar metallic reinforcing elements which are embedded in concrete. The starting material may be commercially avail-able rolled steel wire or a steel Wire of specific composition. Another very important advantage of my process is that the straightening operation takes place, or can take place, simultaneously with highly desirable changes in strength characteristics of steel wire. Thus, and if a concrete reinforcing mat should consist of straight rods having a tensile strength of at least 50 kg./mm.2, such tensile strength can be obtained by starting with coiled wire whose tensile strength is substantially less and by thereupon treating and straightening the wire in accordance with my process whereby the higher tensile strength is a result which is incidental to highly accurate straightening of steel wire. In other words, one can start with a coiled metallic material whose strength characteristics are less than satisfactory for a specific purpose, and the straightening operation will automatically result in a substantial improvement in strength characteristics so that the straightened material is ready for the specific purpose without necessitating any additional treatment with a view to improve its tensile strength, to improve its yield strength and/or to improve each of these characteristics.

In one ofV its simplest forms, the apparatus of my invention comprises first straightening means for continuously or intermittently flexing stock which is withdrawn from a source of supply of coiled wire or the like back Vand forth in one or more planes to effect partial straightening of the stock, and second straightening means for stretching such partially straightened stock with resultant final straightening thereof. The tirst straightening means may comprise one or more sets of exing rolls and the second straightening means may comprise drums which rotate at diiferent speeds or a plurality of clamping devices at least one of which is movable toward and away from the other clamping device or devices in directions which are parallel with the path in which the stock is led past the two straightening stations.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its -mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specic embodiments with reference to the accompanying drawings, in which:

FIG. 1 is a side elevational View of an apparatus which is constructed and assembled for continuous straightening of steel wire and is provided with a cutting device which subdivides straightened stock into pieces of requisite length;

FIG. 2 is a similar side elevational view of modified apparatus wherein the cutting device is replaced by a `storing or take-up drum;

FIG. 3 is a side elevational view of a third apparatus which is constructed and assembled for intermittent straightening of coiled wire;

FIG. 4 is a top plan View of a clamping device which may be utilized in the apparatus of FIG. 3, a portion of the clamping device being shown in section;

FIG. 5 is a fragmentary longitudinal section through a modified clamping device which comprises several pairs of aligned clamping jaws; and

FIG. 6 is a transverse section as seen in the direction of arrows Ifrom the Vline VI-VI of FIG. 5.

Referring to the drawings, and first to FIG. 1, there is shown a rst straightening apparatus which is utilized to straighten steel wire 11 in a continuous operation, i.e., at the same rate at which such wire is being withdrawn and uncoiled from a source of supply here shown as containing a large number of convolutions or coils 13 which are stored on a rotary pay-out reel 12. On its way to a cutting station 18, the wire 11 is advanced along a predetermined path past a first straightening station 14 accommodating two serially arranged primary straightening units 14a, 1417 respectively comprising a plurality of suitably distributed rolls 14C, 14. These rolls serve to repeatedly ex the wire 11 in two different planes whereby the wire undergoes a preliminary straightening treatment and thereupon advances past a braking station 1S which accomodates a large-diameter rotary braking drum 21. The rolls 14C flex the wire 11 back and forth in a plane which coincides with the plane of FIG. l, and the rolls 14d ex the wire back and forth in a plane which is normal or substantially normal to that of FIG. 1. The braking drum 21 serves to advance the wire 11 at a iirst speed, and the thus advanced wire thereupon moves past a drawing or stretching station 17 which accommodates a driven member here sh-own as a drawing or stretching drum 22. The purpose of the drum 22 is to advance the wire 11 at a speed which exceeds that of the drum 21, ie., the drum 21 opposes the advancing action of the drum 22, so that a section 11b between the drums 21, 22 is subjected to tensional stresses and its length increases by at least 2 percent, depending `on the nature of the material of which the wire consists and also whether or not the operation should result in mere straightening or in straightening and simultaneous improvement in strength characteristics of the stock. The thus straightenened section 11b then advances to the cutting station 18 and is subdivided into pieces of desired length, preferably of such length that the pieces may be put to immediate use in concrete molds or for the production of reinforcing mats which are embedded in concrete. The wire 11 is coiled around the drums 21, 22 but the diameters of these drums are so large that the wire is bent well within the elastic limits of its material, i.e., the section 11a which has advanced beyond the drum 22 is absolutely straight. In other words, the radius of curvature of that portion of the wire which is coiled around the drum 22, is so large that such coiling of the wire does not destroy the straightening effect of tensional stresses to which the section 11b is subjected in the zone between the drums 21 and 22.

In the apparatus of FIG l, the construction of the braking drum 21 is preferably identical with that of the stretching drum 22. The drum 22 is driven by a suitable electric or other motor (not shown) through the intermediary of an innitely variable-speed transmission 23. YThe braking drum 21 is driven by a second infinitely variable-speed transmission 24 which is preferably coupled to and derives motion from the transmission 23 or vice versa. The shaft 25 represents an operative connection between the transmissions 23 and 24. As stated above, the' r.p.m. of the drum 21 is less than the r.p.m. of the drum 22 so that the section 11b of the wire 11 is stretched to a desirable degree, and the extent of such stretching may be regulated with requisite precision by changing the speed of the transmission 23 and/or 24. Thestraightened section 11b then advances along supporting rolls 26 and onto rolls 18C provided on the carriage 18b of a cutting device 18a which is mounted on wheels 18d and travels along fixed guideways or rails 18e. When the leading end of the foremost section 11a reaches a stop 18f,the carriage 18b begins to travel at the exact speed of the sections 11a, 11b and its cutter mechanism 18g severs a piece of desired length which may be varied as desired so that the thus severed piece may be put to immediate use. As a rule, the carriage 18b will be provided with one or more automatic ejecting or transfer devicesv (not shown) which remove or eject the severed piece laterally so that the carriage may return to its starting position in -order to be ready for severing of the next-following straightened portion of the wire 11. The carriage 18 b may be flanked by one or more magazines, for example, by suitable racks, on which the ejected pieces are stored and from which such pieces are transported to the next processing station.

The peripheral face lof the drum 21 and/or 22 may be coated with liners or mantles of wear-resistant friction-generating elastic material to prevent deformation of ribs on the wire 11. AS a rule, such liners are necessary only if the diameters of the drums 21, 22 are relatively small. If the diameters of these drums are rather large, the specific pressure between their peripheries and the adjoining portions of the wire 11 is less than the pressure which could result in deformation of the ribs. It is further obvious that the peripheral faces of the rolls 14C, 14d may be provided with similar elastic liners or mantles to avoid deformation of the wire during ilexing. The liners preferably consist of suitable synthetic plastic material which is suiciently resistant to wear to withstand substantial and repeated compression and frictional engagement with smooth-surfaced and/or ribbed metallic rod stock.

The apparatus of FIG. 2 also operates without interruptions and differentiates from the apparatus of FIG. l in the following respects: The braking station 15 is replaced by a braking station 16 which is located ahead of a modified first straightening station 14 and accommodates a braking device 16a including a lixed support 30 for pairs of cooperating braking rollers 31. The straightening station 14 accommodates a primary straightening unit 14a comprising a stationary support 14e for rolls 14e` which ex the wire 11 back and forth in a plane coinciding with the plane of FIG. 2. The drive for the braking rollers 31 is coupled to the drive for the drawing or stretching drum 22 in a manner analogous to that which was described in connection with the transmissions 23, 24, and the speed of the drum 22 exceeds that of the braking rollers 31 so that the section 11b of the wire 11 is stretched to a desired extent. The thus stretched and fully straightened section 11e of the wire 11 is then stored on a take-up reel 32 which is accommodated at a storing station 19. The diameter of the reel 32 is so large that the convolutions 33 of the section 11r, undergo deformation which is well within elastic limits of the wire, i.e., the wire will straighten itself out as soon as the convolutions 33 are removed from the drum 32.

The braking rollers 31 are preferably provided with layers or mantles of relatively soft, wear-resistant, friction-generating elastic plastic material to avoid deformation of longitudinally extending projections or ribs (not shown) which are provided on the wire 11. It is clear that the braking station 16 of FIG. 2 may be located past the primary straightening station 14', and it is also clear that the drum 32 may be replaced by a cutting device of the type or similar to that shown in FIG. 1. The drum 32 is driven to take up the section 11c at the same rate at which this section 4advances past the stretching station 17, and the diameter of the drum 32 preferably exceeds the diameter of the drum 22.

Instead of providing the braking rollers 31 with liners of elastic material, the number of such rollers may be increased to make sure that, despite a relatively low pressure between each braking roller and the adjoining portion of the wire 11, the braking device 16a is still capable of preventing slippage of the wire 11. In other words, all that counts is to insure that the friction between the rollers 31 (which may but need not be provided with elastic liners or mantles) and the wire 11 suffices to enable the drum 22 to bring about requisite elongation of the section 11b.

The apparatus of FIG. 3 is utilized for intermittent straightening of steel wire 11. Preferably, the apparatus will stretch sections having a length corresponding to the length of pieces which are used in concrete molds or in the manufacture of concrete reinforcing mats. The wire 11 is uncoiled from a reel 12 and is led between the rolls 14C of a primary straightening unit 14a which is accommodated at the first straightening station 14. The station 14 is followed by a stationary clamping or gripping device 41 which comprises two clamping jaws 46 and is adapted to temporarily grip the partially straightened section 11d of the wire 11. The section 11d extends forwardly and between the jaws 45 of a reciprocable clamping or gripping device 42 which is located past and is suitably spaced from the clamping device 41. This movable second clamping device 42 comprises a carriage 44 whose w'heels 44a travel on rails provided on a stationary platform or base 48. The base 4S also supports the supporting structure 14e for the rolls 14C and the frame of the clamping device 41. The pairs of jaws 45, 46.are respectively movable toward and away from each other by meansl of actuating devices preferably including suitable hydraulic cylinder and piston assemblies, not shown, so that they may grip or release that portion of the wire 11 which is momentarily located between the corresponding pairs of jaws. In other words, when the carriage 44 of the second clamping device 42 is caused to move away from the stationary clamping device 41, the jaws 45, 46 should not slip with reference to the wire so that the section 11d is stretched and its length increases to a desired extent. Such straightening or extension results in improved strength characteristics and/ or in nal straightening of the section 11d. v

The means for reciprocating the carriage 44 in the longitudinal direction of the section 11d comprises a double-acting hydraulic cylinder 47 which is connected to a bracket 47a on the base 48, and a piston which is reciprocable in the cylinder 47 and whose rod 47b is coupled to the carriage 44. It is clear that the position of the cylinder 47 and piston rod 47b may be reversed. The strokes of the piston rod 471: may be controlled and changed with requisite precision to thereby control changes in length of the section 11d.

The apparatus of FIG. 3 further comprises a pair of feed Vrolls 49 which are located past the reciprocable clamping device 42 and are driven intermittently to withdraw from the reel 12 a fresh section 11d when the jaws 46, 45 of the clamping devices 41, 42 are respectively moved away from each other. The rolls 49 are followed by the table 51 of a cutting device whose cutter mechanism 52 will sever a piece 11e of desired length. The table 51 and/or the cutter mechanism 52 is preferably movable in directions indicated by the doubleheaded arrow 51a so that the operator may select the length of the piece 11e. The drive for the feed rolls 49 is a-lso adjustable in order to enable the operator to select the length of the sections 11d. It is clear that the table 51 may be provided or combined with a suitable ejecting device which removes the pieces 11e following each cutting stroke of the mechanism 52. Such ejecting device will transfer the pieces 11e onto a conveyor or into a magazine, not shown.

The apparatus shown in FIGS. 1, 2 and 3 are preferably provided with suitable control systems including switches, valves, relays or similar auxiliary equipment which will insure that the operation of vvarious units is fully synchronized and that the wire 11 may be straightened or straightened and otherwise treated with a minimum of supervision. For example, and referring to FIG. 3, the movements of jaws 46, 45, the movements of the carriage 44, the rotation of feed rolls 49 and the movements of the cutter mechanism 52 may be regulated by a hydraulic control system so that the apparatus will furnish straightened pieces 11e of wire 11 at desired intervals. j

The gripping faces of the jaws 45, 46 are preferably provided with liners of elastically deformable, wearresistant friction-generating plastic or other material to avoid undesirable deformation of ribs on the wire 11. The Ilength of the jaws 45, 46 (as seen in the longitudinal direction of the wire 11) must be sucient to prevent slippage between their liners and the section 11d when the clamping device 42 is moved in a direction to the right (see the arrow 11x) in FIG. 3, and when the aforementioned hydraulic cylinder and piston assemblies respectively maintain the jaws 45, 46 in clamping engagement with the wire 11.

Some or all of the rolls 14e may be driven at the time when a predetermined length of wire 11 advances in response to rotation of the feed rolls 49. The drive for some or all of the rolls 14C may be coupled to the drive for the rolls 49. The hydraulic drive 47, 47b for the carriage 44 may be replaced by an electric motor or the like. For example, the electric motor may drive a mechanical reciprocating device including a rotary spindle which meshes with a spindle nut secured to the carriage 44. The spindle is held against axial movement so that, whenever it rotates, the nut and the carriage will be compelled to move in or counter to the direction indicated by the arrow 11x. It is also possible to replace such spindle with a toothed rack which is fixed to the carriage 44 and meshes with a pinion driven by a reversible motor.

It is further possible to construct the improved apparatus in such a way that the wire 11 may be straightened continuously or intermittently, depending on the output of the machines which receive straightened pieces from the apparatus. For example, the movable clamping device 42 of FIG. 3 could be replaced by a` device including a pair of endless chains provided with suitably spaced clamping jaws which may engage and stretch the wire whenever the chains are driven. Depending upon whether the chains are driven continuously or at intervals, the jaws will bring about continuous or intermittent stretching of the wire. Such clamping device can be placed past the stationary clamping device 41 of FIG. 3, past the braking drum 21 of FIG. l (to replace the drum 22), past the braking device 16a of FIG. 2 (to replace the drum 22) or past the drum 22 of FIG. l or 2.

The apparatus shown in FIGS. 1 to 3 may be combined with a suitable twisting device which will spin the wire 11 so that the originally straight ribs of the wire will resemble helices. In the apparatus of FIG. 3, the jaws 45 of the movable clamping device 42 may lbe rotated about the axis of the wire 11 so that the section 11d between the jaws 46, 4S is automatically twisted during stretching. The drive which rotates the jaws 45 may include a variab-le-speed electric or hydraulic motor mounted on the carriage 44 of the clamping device 42.

The feed rolls 49 of FIG. 3 are preferably located immediately past the clamping device 42 when the carriage 44 reaches its right-hand end position. As stated hereinabove, the drive for the feed rolls 49 operates intermittently and is actuated only at such times when the clamping jaws 46, 45 are disengaged from the wire 11 so that the freshly straightened section 11d may be advanced onto the table 51 and that a predetermined length of Wire is uncoiled and withdrawn from `the reel 12 to pass between the rolls 14e of the primary straightening unit 14a at the station 14.

The jaws 45 and 46 act not unlike a pair of tongs and grip the wire 11 from opposite sides.

FIG. 4 illustrates a clamping device which is provided with safety means for preventing excessive stretching of wire. Basically, the clamping device of FIG. 4 is constructed and assembled in such a way that, in response to a certain force transmitted by the wire 11 in the axial direction thereof, at least one of the clamping jaws 46a, 461; will move with reference to its holder 61a, 61b in the direction indicated by the arrow 11x, i.e., in the direction of lengthwise movement of the wire. The holders 61a, 61b are movable toward or away from each other (see the arrows 61A, 61B) or at least one of these holders is movable with reference to the other holder so that the Wire 11 may be clamped or released. The jaws 46a, 46h comprise slidable portions 62a, 62b which are guided by ways 63a, 63h on the holders 61a, 61b, and these holders respectively comprise stops 67a, 67h which limit movements of the corresponding jaws in the directions indicated by the arrow 11x. The slidable portions 62a, 62h are provided with toothed racks which mesh with pinions 65a, 65b rigidly mounted on shafts 66a, 66h. 'Ihe shafts 66a, 66b are mounted in the holders 61a, 61b and their axes are normal to the axis of the wire 11. Each of these shafts is connected with a suitable braking device (not shown) which prevents rotation of the respective pinion until and unless the force acting in the direction of the arrow 11x overcomes the braking force. The braking devices are adjustable so that the jaw 46a and/or 46b will advance with the wire 11 in response to a predetermined tensional stress upon the wire. The forward move-ment of the jaws 46a, 4Gb is terminated when their holders 62a, 62h respectively engage the stops 67a, 67b.

The clamping device yof FIG. 4 may be used as a substitute for the clamping device 41 and/ or 42 of FIG. 3.

Referring finally to FIGS. 5 and 6, there is shown a portion of a further clamping device which comprises two holders 71 (only one shown). The holder 71 which is actually shown in FIGS. 5 and 6 is movable toward (arrow 71A) and away from the other holder so that it moves nearer to or away from a steel wire 11. The underside of the holder 71 is provided with a longitudinally extending groove or recess 72 of triangular cross section which receives slidable portions 74 of three serially arranged clamping jaws 73a, 73h, 73C. The leftmost jaws 73a is adjacent to a rear stop 75 which is rigid with the holder 71. A horizontal guide rod 76 is fixed to the rear stop 75 and to a front stop 79 to extend in parallelism with the wire 11. The jaws 7Bm-73C are slidable on the rod 76 and the foremost jaw 73e is biased by a prestressed helical spring 78 which surrounds a portion of the rod 76. The numeral 77 denotes a bore in the foremost jaw 73e which receives a portion of the guide rod 76 and registers with similar bores of the jaws 73a, 73h. The front stop 79 constitutes a retainer for the foremost convolution of the spring 78.

The jaws 73a-73c are respectively provided with clamping faces 80a, 80h, 80e of diminishing area so that the clamping force of the median jaw 73h exceeds that of the foremost jaw 73e but is less than the clamping force of the rearmost jaw 73a. This allows for stretching of that portion of the wire 11 which extends between the stops 75, 79 because the jaws 73a-73c are movable with reference to each other.

The clamping device of FIGS. 5 and 6 may replace the reciprocable clamping device 41 shown in FIG. 3. When the jaws 73a-73c (and the complementary jaws of the non-illustrated second holder) grip the wire 11 and the carriage 44 of the second clamping device 42 is moved in the direction indicated by the arrow 11x, the foremost jaw 73e,` will be the first to slide in the groove 72 in a direction toward the front stop 79 whereby its wedgelike portion 74 slides relative to the holder 71 with a friction determined by the force which urges the face 80e` into engagement with the wire 11. The median jaw 7311 follows but covers a shorter distance in the axial direction of the guide rods 76, and the rearmost jaw 73a will cover the shortest distance.

It is obvious that the clamping device of FIGS. 5 and 6 may be modified by providing the jaws 73a-73c with slidable portions 74 of different size so that the friction between the surface surrounding the groove 72 and such slidable portions varies from jaw to jaw. In such clamping devices, all of the faces 80a-80c on the clamping jaws may have the same area.

FIG. 6 shows a portionof the rearmost jaw 73a' which is slidable in the V-shaped groove of the second holder, and this second holder is preferably mirror symmetrical with reference to the holder 71.

Many heretofore known straightening apparatus will operate more or less satisfactorily if the diameter of the wire does not exceed a certain value, normally 8 mm. If such known apparatus are used for straightening of relatively thick wires or rods, and if such relatively thick rods or wires are provided with ribs, the ribs will undergo excessive deformation so that the bond between the pieces of straightened material and hardened concrete is too weak. It is well known that the ribs of steel rods which are used in reinforced concrete insure the formation of 9 a very strong bond between metal and concrete. A strong bond can be obtained only if the ribs remain undeforrned, i.e., they should not be flattened or worn away at the time the convoluted stock is subjected to one or more straightening actions.

However, even if a conventional apparatus is used for straightening of rela-tively thin wire or rod stock, the deformation of ribs or similar projections is such that the bond between concrete and the pieces of wire or rod is too weak. Also, the faces of wire-engaging rolls, rollers, drums and/ or jaws which are used in conventional apparatus undergo too much Wear so that they must be replaced at frequent intervals with resultant loss in output and high maintenance cost. Furthermore, many known straigtening apparatus will automatically spin the stock so that the originally straight ribs are twisted. While a controlled twisting of ribs is often desirable, uncontrolled twisting should be avoided because it causes localized weakening of 4the ultimate product. I also contemplate twisting of the wire 11; however, such twisting is uniform so that the strength characteristics of the straightened pieces are uniform in all zones thereof and that such strength characteristics may be determined in advance by controlled rotation of clamping jaws. If the twisting operation is not uniform, it might cause localized brittleness of steel wire, especially if such wire consists oi high quality steel.

Furthermore, many heretofore known apparatus cannot insure accurate straightening of steel wire, and this affects the operation of machines which receive straightened material for further processing. Even minimal deformation of steel wires or rods might result in the production of inferior concrete reinforcing mats or in improper distribution of reinforcing rods in a concrete mold.

It was further found that the flexing action of primary straightening rolls (such as the rolls 14C, 14d shown in FIG. 1) is not sufficient to effect satisfactory straightening of relatively thick steel wire or rod stock, especially if such stock is provided with ribs or similar projections. Excessive flexing or bending is undesirable because it might damage the ribs and because it might result in localized weakening of the meal. Once the diameter of a coiled steel wire exceeds a certain value, flexing rolls by themselves cannot produce a straightening action which would even approximate the requirements in production of reinforced concrete or the like.

My invention is based on the surprising discovery that repeated exing of coiled steel wire or similar metallic rod stock in one or more planes and subsequent stretching of the partially straightened material Will result in highly satisfactory straightening so that the thus processed material may yield absolutely straight pieces of any desired length. As a rule, the rolls (such as the rolls 14C and/ or 14d) of the primary or rst straightening unit will be mounted at a greater distance from each other than in heretofore known flexing devices because such rolls need not bring about full straightening of wire 11 but are used mainly to insure unimpeded and controlled advance of partially straightened material toward and past the second or final straightening station. In other words, the flexing action of rolls 14C and/ or 14d need not be too effective because this is merely a preliminary straightening operation whereas the nal straightening takes place when the wire is stretched between a braking device and a stretching drum or between a pair of relatively movable clamping devices.

When the stretching operation results in relatively small increase in overall length of the thus treated section, the wire or rod will be simply straightened but the strength characteristics of its material need not undergo any significant changes. On the other hand, if the stretching operation results in substantial elongation of the stock, the latter is straightened with simultaneous and highly beneficial changes in its strength characteristics, particularly tensile strength. In other words, by the simple expedient of stretching the wire Y11, one can obtain absolutely straight sections and one can simultaneously improve the tensile strength and certain other strength characteristics of metallic material. As a rule, and if the wire 11 is to oe subjected to a straightening action without desiring to change its strength characteristics, the increase in overall length of each section 11b, 11b' or 11d will be in the range of 2-6 percent. If the elongation is between 2 and 4 percent, the elastic limit yield strength of the material will be higher; however, if the elongation is in the range of 4-12 percent, the elastic limit and tensile strength of the material Will be changed, i.e., the strength characteristics of steel wire will improve and the extent of such improvement will depend (at least to a certain extent) on the composition of the material. It was found that the yield strength and the tensile strength of steel wire will improve considerably if the overall elongation of such wire is between 6-11 percent, particularly be tween 8-10 percent.

Of course, the elongation of steel wire will take place within the elastic limits of its material. The apparatus of my invention may be utilized for straightening of commercially available rolled steel wire; however, I normally prefer to utilize wire having a ycertain composition, particularly as regards its carbon, manganese, silicon, phosphorus and sulphur contents. Thus, the percentage of carbon should be less than 0.2 percent, preferably between 0.l2 and 0.18 percent, and the percentage of manganese should be between 0.25 and 0.60 percent. It was further found that the wire should preferably contain not less than 0.08 percent of carbon. While the percentage of silicon is not too critical, it should preferably approximate 0.2 percent. The percentage of phosphorus and sulphur may be the same as in commerically available rolled steel wire.

The starting material may be killed, semikilled or unkilled steel which is produced in open-hearth, electrolytic or LD furnaces (oxygen-blowing method). The exact percentage of carbon is of particular importance and it should remain within the aforementioned limits. This insures that the wire will have a strength which allows for satisfactory straightening with relatively small increase in length. The exact value of the elastic limit is of lesser importance, and such elastic limit may be influenced by the extent to which theI wire is extended during stretching; therefore, the aforementioned percentage of manganese suices in contrast to so-called self-hardening steels which must contain a higher percentage of manganese. The material which I prefer to utilize in the manufacture of concrete reinforcing mats or in the production of straight rods for use in concrete molds is readily weldable which is important in the production of mats. As disclosed, for example, in my copending applications Serial Nos. 317,- 405, and now abandoned and 430,288, concrete reinforcing mats may be produced in automatic machines by welding longitudinal and transverse rods to each other whereby the machine may form a seam at each intersection or at certain intersections between the longitudinal and transverse members.

As stated before, the total elon-gation of the wire 11 will be selected in such a way that the thus stretched sections of the wire are inerely straightened and/ or undergo changes in their strength characteristics. By changing the length of a section between 2 4 percent, the section will be straight but need not necessarily undergo any significant changes in its strength characteristics. Thus, when the elongation is rel-atviely small, the changes in strength characteristics will be rather negligible but such characteristics will improve considerably if the extent of stretching is increased to 8 percent or higher. For example, the yield strength and tensile strength of a steel wire or rod may be raised from 45 kg./mm.2 -to or above 50 kg./mm.2. The resulting straight lengths of wire are ideally suited for further processing, i.e., they can be shaped just as well or more readily than prior to stretching. Also, and as mentioned above, the tensile strength is higher than the tensile strength of a similar steel stock which has been treated in a conventional manner. The upper limit of elongation is normally around l2 percent, and the preferred range of elongation to effect desirable changes in strength characteristics of straightened material is presently believed to be between 8-10 percent.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is:

1. A process for straightening coiled metallic rod stock, particularly coiled steel wire, comprising the steps of uncoiling a section of such stock and exing the section back and forth in at least one plane to effect partial straightening thereof; and thereupon subjecting such partially straightened section to the action of tensional stresses to increase its overall length by at least two percent with resultant final straightening of the thus stretched section.

2. A process for straightening coiled metallic rod stock, particularly coiled steel wire of the type which is used in reinforced concrete, comprising the steps of uncoiling a section of such stock and flexing each zone of the section back and forth in at least one plane to effect partial straightening thereof; and thereupon subjecting the section to the action of tensional stresses of such magnitude that the overall length of the section increases by 2-6 percent with resultant nal straightening thereof.

3. A process for straightening and improving the strength characteristics of coiled metallic rod stock, particularly for straightening and improving the tensile strength of coiled steel wire, comprising the steps of uncoiling a section of such stock and flexing each zone of the section back and forth in at least one plane to effect par-tial straightening thereof; and thereupon subjecting the section to the action of tensional stresses of such magnitude that the overall length of the section increases by 4-12 percent with resultant final straightening and simultaneous improvement in tensile strength thereof.

4. A process as set forth in claim 3, wherein the magnitude of said tensional stresses is such that the overall length of the section increases by 6-1'1 percent.

5. A process as set forth in claim 3, wherein the magnitude of said tensional stresses is such that the overall length of the section increases by 8-10 percent.

'section increases by at least two percent wi-th resultant final straightening of such sections.

7. A process for straightening coiled metallic rod stock,

particularly for straightening coiled steel wire, comprising the steps of intermittently withdrawing from a source of coiled rod stock sections of predetermined length and flexing each such section back and forth in at least one plane to effect partial straightening of the thus flexed sections; and thereupon subjecting consecutive sections to the action of tensional stresses of such magnitude that lthe overall length of each section increases by at 'least two percent with resultant final straightening of such sections.

8. A process for straightening coiled metallic rod stock,

particularly coiled steel wire, comprising the steps of withdrawing a section of such stock from a source of supply and repeatedly fiexing each zone of the section back and forth in at least one plane to effect partial straightening thereof; and thereupon clamping the ends of the section and moving one end of the section away from the other end to increase its overall length by 2l2 percent with resultant final straightening of the thus stretched section.

9. A process for straightening coiled metallic rod stock, particularly for straightening coiled steel wire of the type provided with external ribs for use in reinforced concrete, comprising the consecutive steps of withdrawing a section from a source of coiled rod stock and flexing each zone of the thus withdrawn section back and forth in at least one plane to effect partial straightening thereof; subjecting the section to the action of tensional s-tresses of such magnitude that the overall length of the section increases by 2-12 percent with resultant final straightening of the thus stretched section; and coiling the thus stretched section to form a loop of such diameter that the deformation of the looped section remains within the elastic limits of its material.

10. A process for straightening coiled metallic rod stock, particularly for straightening coiled steel wire for use in reinforced concrete, comprising the steps of consecutively withdrawing elongated sections from a source of coiled rod stock and flexing each such section back and forth in at least one plane to effect partial straightening thereof; thereupon subjecting each partially straightened section to the action of tensional stresses of such magnitude that the overall length of each section increases by Z-lZ percent with resultant full straightening thereof; and immediately subdividing the fully straightened rod stock into pieces of desired length.

11. A process for straightening coiled steel wire for use in reinforced concrete, comprising the steps of withdrawing and simultaneously uncoi'ling a section from a source of coiled steel Wire containing up to 0.2 percent of carbon and exing each zone of the section lback and forth in at least one plane to effect partial straightening thereof; and thereupon subjecting the section to the action of tensional stresses of such magnitude that the overall length of the section increases by 2-1l2 percent with resultant full straightening thereof.

12. A process as set forth in claim 11, wherein said wire contains between 0.12 and 0.18 percent of carbon.

13. A process for straightening coiled steel wire for use in reinforced concrete, comprising the steps of witl1- drawing and simultaneously uncoiling a section from a source of coiled steel wire containing between 0.25 and 0.60 percent of manganese and flexing each zone of the section back and forth in at least one plane to effect partial straightening thereof; and thereupon subjecting the section to the action of tensional stresses of such magnitude that the overall length of the section increases by 212 percent with resultant full straightening thereof.

14. A process for straightening coiled steel wire for use in reinforced concrete, comprising the steps of withdrawing and simultaneously uncoiling a section from a source of coiled steel wire containing between 0.08 and 0.2 percent of carbon and flexing each zone of the section back and forth in at least one plane to effect partial straightening thereof; and thereupon subjecting the section to the action of tensional stresses of such magnitude that the overall length of the section increases by 2-12 percent with resultant full straightening thereof.

1S. An apparatus for straightening coiled metallic rod stock, particularly for straightening coiled steel wire, comprising first straightening means arranged to iiex the stock back and forth in at least one plane to effect partial straightening thereof; and second straightening me-ans arranged to stretch such partially straightened stock with resultant final straightening thereof.

16. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; means including a driven member for withdrawing -the stock from said source and for advancing the thus withdrawn stock lengthwise along a predetermined path; at least one primary straightening unit adjacent to said path and including a plurality of flexing members arranged to flex the advancing stock back and forth in atleast one plane to effect partial straightening thereof; and braking means adjacent to said path and arranged to oppose the advancing action of said driven member whereby a section of said stock which extends between said braking means and said driven member is subjected to tensional stresses of such magnitude that its length increases with resultant final straightening thereof.

17. An apparatus as set forth in claim 16, wherein Said driven member is :a stretching drum and the stock is convoluted about and is held in frictional engagement with the periphery of said drum, the diameter of said drum being such that the flexing of stock which is convoluted therearound remains within the elastic limits of its material.

18. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising =a source of coiled stock; means including a driven member for withdrawing the stock from said source and for advancing the t-hus withdrawn stock lengthwise along a predetermined path; at least one primary straightening unit adjacent to said path and comprising means for flexing the advancing stock back and forth in at least one plane for effecting partial straightening thereof; and braking means adjacent to said path intermediate said source and said primary straightening unit and arranged to oppose the advancing action of said driven member whereby a sec` tion of said stock which extends between said braking means and said driven member is subjected to tensional stresses of such magnitude that its length increases with resultant nal straightening thereof.

19. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; means including a driven member for withdrawing the stock from said source and for advancing the thus withdrawn stock lengthwise along a predetermined path; at least one primary straightening unit adjacent to said path and comprising means for flexing the advancing stock back and -forth in at least one plane for effecting partial straightening thereof; and braking means adjacent to said path intermediate said driven vmember and said primary straightening unit and arranged to oppose the advancing action of said driven member whereby `a section of said stock which extends between said braking means and said driven member is subjected to tensional stresses of such magnitude that its length increases with resultant nal straightening thereof. Y

20. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; means including a driven member for withdrawing the stock from said source and for advancing the thus withdrawn stock lengthwise along a predetermined path; at least one primary straightening unit adjacent to said path and comprising means for flexing the `advancing stock back and forth in at least one plane for effecting partial straightening thereof; and braking means adjacent to said path and arranged -to oppose the advancing action of said driven member whereby a section of said stock which extends between said braking means and said driven member is subjected to tensional stresses of such magnitude that its length increases with resultant final straightening thereof, said braking means comprising a rotary braking drum and a portion of said section being convoluted around the periphery of said braking drum.

21. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; means including a driven member for withdrawing the stock from said source and for advancing the thus withdrawn stock lengthwise along a predetermined path; at least one primary straightening unit adjacent to said path and comprising means for flexing the advancing stock back and forth in at least one plane for effecting partial straightening thereof; and braking means adjacent to said path and arranged to oppose the advancing action of said driven member whereby a section of said stock which extends between said braking means and said driven member is subjected to tensional stresses of such magnitude that its length increases with resultant nal straightening thereof, said braking means comprising at least one pair of cooperating braking rolls arranged to engage the stock and being located at a predetermined distance from said driven member, said driven member comprising a driven drum and a portion of said section being trained around the periphery of said drum.

22. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; a feed for intermittently withdrawing sections of desired length from said source and for advancing such sections lengthwise along a predetermined path; a primary straightening unit adjacent to said path and arranged to flex each section back and forth in at least one plane to effect partial straightening thereof; and a first and a second clamping device adjacent to said path between said unit and said feed and each comprising cooperating jaws movable into clamping engagement with a section during the intervals between intermittent operations of said feed, said clamping devices being spaced from each other longitudinally of said path and one thereof being movable away from the other clamping device to lengthen the stock between said clamping devices with resultant final straightening of the thus extended stock. y

23. An apparatus as set forth in claim 22, wherein said primary straightening unit comprises a plurality of flexing rolls and wherein said rolls are distributed length-- wise of said path and at a considerable distance from each other, v

24. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled Stock; a feed for intermittently withdrawing sections of desired length from said source and `for advancing such sections lengthwise along a predetermined path; a primary straightening unit -adjacent to said path land arranged to flex each section back and forth in at least one plane to effect partial straightening thereof; a rst and a second clamping device adjacent to said path between said unit and said feed and each comprising cooperating jaws movable into clamping engagement with a section during the intervals between intermittent operations of said feed, said clamping devices being spaced from each other longitudinally of said path and one thereof being movable away from the other clamping device to lengthen the stock between said clamping devices with resultant final straightening of the thus extended stock; and hydraulic reciproc-ating means for said one clamping device.

25. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; a feed for intermittently withdrawing sections of desired length from said source and for advancing such sections lengthwise -along a predetermined path; a

vprimary straightening unit adjacent to said path and arranged to flex each section back and forth in at least one plane to effect partial straightening thereof; .a first and a second clamping device adjacent to said path between said unit and said feed and each comprising costock; a feed for intermittently withdrawing sections of desired length from said source and for advancing such sections lengthwise along a predetermined path; a primary straightening unit adjacent to said path and arranged to ex each section back and forth in at least one plane to effect partial straightening thereof; a first and a second clamping device adjacent to said path between said unit and said feed and each comprising cooperating jaws movable into clamping engagement with a section during the intervals between intermittent operations of said feed, Said clamping devices being spaced from each other longitudinally of said path and one thereof being movable away from the other clamping device to lengthen the stock between said clamping devices with resultant final str-aightening of the thus extended stock; and means for twisting that length of stock which extends between and is ciamped by the jaws of said clamping devices.

27. An apparatus as set forth in claim 26, wherein the jaws of said one clamping device are rotatable about the axis of the stock and wherein said twisting means comprises a drive for rotating said last named jaws about such axis.

28. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; a feed including at least one pair of driven feed rolls spaced from said source and having faces for intermittently withdrawing sections of desired length from said source and for advancing such sections lengthwise along a predetermined path; a primary straightening unit adjacent to said path and arranged to iiex each section back and forth in at least one plane to effect partial straightening thereof; and a rst and a second clamping device adjacent to said path between said unit and said feed and each comprising cooperating jaws movable into clamping engagement with a section during the intervals between intermittent operations of said feed, said clamping devices being spaced from each other longitudinally of said path and one thereof being movable away from the other clamping device to lengthen the stock between said clamping devices with resultant final straightening of the thus extended stock.

29. An apparatus as set forth in claim 28, wherein said feed rolls are closely adjacent to said one clamping device when the latter is moved away from said other clamping device and further comprising cutting means located past said feed rolls for subdividing the fully straightened stock into pieces of desired length.

30. An apparatus as set forth in claim 29, wherein said cutting means comprises a supporting table and a cutting device mounted on said table.

31. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; a feed for intermittently withdrawing sections of desired length from said source and for advancing such sections lengthwise along a predetermined path; a primary straightening unit adjacent to said path and arranged to flex each section back and forth in at least one plane to effect partial straightening thereof; and a first and a second clamping device adjacent to said path between said unit and said feed and each comprising cooperating tonglike jaws movable into clamping engagement with a section during the intervals between intermittent operations of said feed, and hydraulic actuating means for moving the jaws of each clamping device toward and away from each other, said clamping devices being spaced from each other longitudinally of said path yand one thereof' being movable away from the other clamping device to lengthen the stock between said clamping devices with resultant final straightening of the thus extended stock.

32. An apparatus for straightening coiled steel wire or similar metallic rod stock, comprising a source of coiled stock; a feed for intermittently withdrawing sections of desired length from said source and for advancing such sections lengthwise along a predetermined path; a primary straightening unit adjacent to said path and arranged to fiex the sections back and forth in at least one plane to effect partial straightening thereof; and a first and a second clamping device adjacent to said path between said unit and said feed and each comprising cooperating clamping means movable into clamping engagement with a section during the intervals between intermittent operations of said feed, said clamping devices being spaced frorn each other longitudinally of said path and said first clamping device being movable away from said second clamping device to lengthen the stock between said clamping means with resultant nal straightening of the thus extended stock.

33. An apparatus as set forth in claim 32, wherein at least one of said clamping devices further comprises a pair of holders and wherein the clamping means of said one clamping device comprises at least one clamping jaw for each of said holders, at least one of said jaws being movable with reference to the corresponding holder in the longitudinal direction of said path, and safety means for retaining said one jaw against movement with reference to the corresponding holder when the stress transmitted by the extending stock remains below a predetermined value so that said one jaw automatically follows the movement of stock in response to excessive stresses such as could result in overextension of the stock.

34. An apparatus as set forth in claim 33, wherein said safety means comprises an adjustable braking device so that said predetermined value of stresses transmitted to said one jaw by extending stock may be selected at the will of the operator.

3S. An apparatus as set forth in claim 32, wherein at least one of said clamping devices further comprises a pair of holders including elongated guide means extending in the longitudinal direction of said path and wherein the clamping means of said one clamping device comprises two sets of clamping jaws each mounted in and movable longitudinally of one of said guide means, and stop means for limiting the movement of said jaws with reference to the corresponding holders.

36. An apparatus as set forth in claim 35, wherein each of said holders is provided with an elongated V- shaped groove extending in the longitudinal direction of said path and wherein each of said clamping jaws comprises a wedge-like portion which is slidable in the respective groove.

37. An apparatus as set forth in claim 35, further comprising resilient means mounted on at least one of said holders and arranged to oppose movement of the respective jaws in response to extension of said stock.

38. An apparatus as set forth in claim 35, wherein the jaws of each set comprise stock-engaging faces of different areas.

39. An apparatus as set forth in claim 38, wherein the areas of said faces diminish in the direction in which the stock is extended in response to movement of said first clamping device away from said second clamping device.

40. An apparatus for straightening coiled metallic rod stock, particularly for straightening coiled steel wire,

comprising first straightening means for flexing the stock back and forth in at least one plane to effect partial straightening thereof; and second straightening means for stretching such partially straightened stock with resultant nal straightening thereof, at least one of said straightening means comprising at least one member having a stock-engaging portion consisting of elastically deformable friction-generating material.

41. An apparatus* as set forth in claim 40, wherein said second straightening means comprises a fixed and a movable clamping device each having a plurality of clamping jaws, at least some of said clamping jaws hav- 'ing stock-engaging liners consisting of elastically deformable friction-generating material.

42. An apparatus as set forth in claim 40, wherein said second straightening means comprises a pair of V1'2' spaced rotary drums and means for driving said drums at different speeds, said stock being convoluted around each of said drums and at least one of said drums having a peripheral liner of elastically deformable friction-generating material which engages the convoluted portion of the stock.

43. An apparatus as set forth in claim 40, further comprising a feed for advancing the stock from a source of supply past said first and second straightening means, said feed including a plurality of driven rolls and at least some of said rolls having peripheral mantles consisting of elastically deformable friction-generating material which engages and advances the stock in response to rotation of said rolls.

44. An apparatus as set forth in claim 40, wherein said second straightening means comprises a plurality of braking rolls and wherein at least some of said braking rolls comprises peripheral liners of elastically deformable friction-generating material which engages the stock.

45. An apparatus for straightening coiled metallic rod stock, particularly for straightening coiled steel wire, comprising first straightening means for exing the stock 18 back and forth in at least one plane to etfect partial straightening thereof; second straightening means for stretching such partially straightened stock with resultant final straightening thereof; and storing means comprising a rotary take-up drum located past said second straightening means for collecting and convoluting the finally straightened stock, the diameter of said drum being such that the convolutions thereon are exed within the elastic limits of said stock.

46. An apparatus as set forth in claim 45, wherein said second straightening means comprises means for continuously withdrawing coiled stock from a source of supply and wherein said drum is driven at the exact speed of finally straightened stock.

References Cited UNITED STATES PATENTS 1,894,703 l/1933 Pierce 72-160 CHARLES W. LANHAM, Primary Examiner. R. D. GREFE, Assistant Examiner. 

1. A PROCESS FOR STRAIGHTENING COILED METALLIC ROD STOCK, PARTICULARLY COILED STEEL WIRE, COMPRISING THE STEPS OF UNCOILING A SECTION OF SUCH STOCK AND FLEXING THE SECTION BACK AND FORTH IN AT LEAST ONE PLANE TO EFFECT PARTIAL STRAIGHTENING THEREOF; AND THEREUPON SUBJECTING SUCH PARTIALLY STRAIGHTENED SECTION TO THE ACTION OF TENSIONAL STRESSES TO INCREASE ITS OVERALL LENGTH BY AT LEAST TWO PERCENT WITH RESULTANT FINAL STRAIGHTING OF THE THUS STRETCHED SECTION. 